1. Field of the Invention
The present invention relates to a base transceiver station and channel rate control method used in a radio communication system using an HSDPA (High Speed Downlink Packet Access) communication scheme.
2. Description of Related Art
Conventionally, systems using the HSDPA communication scheme have been known in radio communication systems including base transceiver stations. The radio communication system using the HSDPA communication scheme is constructed of a radio access network comprised of a radio network controller (RNC) and base transceiver station (BTS) lying below the radio network controller, and mobile terminals (UE: User Equipment) connected to the radio access network, varies throughput corresponding to radio environments of the mobile terminals and the number of connected terminals, and thereby actualizes improvements in radio utilization efficiency and high-speed transmission.
Further, in the radio communication system using the HSDPA communication scheme, since the throughput varies corresponding to radio environments of the mobile terminals and the number of connected terminals, problems occur that the data detention amount increases in the base transceiver station when the transmission rate between the radio network controller and base transceiver station is higher than the transmission rate in the radio channel and that utilization efficiency degrades in the radio channel when the transmission rate between the radio network controller and base transceiver station is lower than the transmission rate in the radio channel. To solve the problems, in the radio communication system using the HSDPA communication scheme, flow control is performed between the radio network controller and base transceiver station in accordance with the transmission rate in the radio channel.
More specifically, the base transceiver station calculates transmission quality based on the amount of data loss such as a break, dropout, discard, etc. of data between the base transceiver station and radio network controller, while further calculating radio quality based on throughput predicted from radio environments of mobile terminals and the number of connected terminals and the detention amount of the buffer in the base transceiver station, calculates permissible data amount for the radio network controller to transmit to the base transceiver station from the channel quality and radio quality, notifies the permissible data amount to the radio network controller, and thereby controls the transmission data amount from the radio network controller.    [Patent Document 1] Japanese Laid-Open Patent Publication No. 2008-053851
However, in the radio communication system as described above, there is a possibility of malfunctions in other functions such as call control processing, monitoring control and the like as well as the reception function in the base transceiver station when the radio network controller transmits the data amount exceeding the processing capability of the base transceiver station to the base transceiver station. Particularly, indoor-use small-size base transceiver stations are designed to low processing capability, and therefore, have the possibility of malfunctioning.